Evidence for an Exotic Baryon State, Theta+(1540), in Photoproduction Reactions from Protons and Deuterons with CLAS

Abstract

CLAS photoproduction data on deuterium and hydrogen targets have been analyzed in a search for an exotic baryon state with strangeness S=+1, the \Theta^+ (originally named the Z^+). This resonance was predicted recently in theoretical work based on the chiral soliton model as a lowest mass member of an anti-decuplet of 5-quark states. The reaction gamma d --> pK^-K^+n, which requires a final state interaction inside the deuteron, was used in the analysis of deuteron data. In the analysis of proton data, the reaction gamma p --> pi^+K^-K^+n was studied. Evidence for the \Theta^+ state is found in both analyses in the invariant mass distribution of the nK^+. Our results are consistent with previously reported results by LEPS/Spring-8 collaboration (Japan), and by the ITEP (Moscow) group.